I assume you're talking about in nature. Keep in mind that most of the "wave" is underwater, like an iceberg. The reef takes the legs out from under the wave causing it to break.
Hope that's what you were asking.
Take care,
Dan'l
YEAH, that's what I was looking for. I always thought the water going back into the ocean went under the wave causing it to have a collision, thus making the wave, but I didn't how it worked with a coral reef